1. Technical Field
The present invention relates to enhanced oil recovery in tertiary oil recovery, especially to a microorganism for oil displacement and a composite oil displacement agent containing the microorganism.
2. Background
Over 40% of underground crude oil still remains in the formation after primary and secondary oil recovery; and even 80% of crude oil could remain in the formation after primary and secondary oil recovery if the formation conditions are not ideal. So far, the main oilfields in our country have undergone high water cut stage and underground crude oil has been under the discontinuous dispersed state, the oil displacement technology is mainly featured by utilizing the synergistic effect of alkaline, polymer and surfactant to reach the effects of increasing oil production increasing and reducing water, in order to enhance the recovery rate of crude oil.
Alkaline/polymer/surfactant trinary composite oil displacement system, though capable of enhancing the recovery rate of crude oil remarkably, has been accompanied by some questions in the process of large-scale industrial application: 1) the use of alkaline could lead to the precipitation of multivalent ions and the corrosion of rock and minerals, further destroying the structure of oil layer and oil well and severely damaging the formation, besides, the pump barrel needs to be cleaned once every 10 to 15 days, so the oil. recovery cost is increased; 2) the presence of alkaline can not only increase the usage of polymer dramatically, but also reduce the viscoelasticity of polymer greatly, especially the elasticity of polymer; and 3) the use of alkali could further cause the situation that the produced liquid is W/O type emulsion with higher viscosity, which not only impacts on oil well productivity, but also raises the difficulty of demulsification.
It is found by retrieval that one of three patent documents related to the present invention, CN1580486, discloses an oil displacement method, which sequentially comprises the following steps of: culturing at least one of Bacilluscereus HP, CGMCC No. 1141 and Brevibacillus brevis HT, CGMCC No. 1142 in a culture medium with crude oil as carbon source to obtain fermentation liquid; injecting the resultant fermentation liquid in the oil layer for 3 to 5 days; and then using a trinary composite system for oil displacement; according to the present invention, physical properties of crude oil are improved after microorganism fermentation liquid derived from. HP and HT is used for affecting the crude oil, the affected crude oil has reduced interfacial tension of prior trinary prescription compared with unaffected crude oil, the microorganism fermentation liquid is 2 to 12 times diluted and then added with a small amount of alkylbenzene sulfonates surfactant S1 (0.01 wt % to 0.04 wt %), the interfacial tension can reach 10-3 mN/m, the cost is greatly reduced and the crude oil has excellent stability. The patent application CN101544885 discloses a composite microorganism oil displacement agent for enhancing the oil recovery rate of crude oil, which is formed by adding mixed liquid, consisting of 1 to 8 wt. % of cereals-processing byproduct, 0.5 to 6 wt. % of wood-processing byproduct, with 5 to 10 mg/L of trace elements and 300 to 500 mg/L of polyacrylamide, wherein the agriculture/wood-processing byproducts have the particle diameter smaller than 0.5 mm. CN1504529 discloses a thick oil emulsification viscosity reducer, comprising: 1) anionic surfactant selected from the group consisting of petroleum sulfonate formaldehyde condensate and lignin sulphonate, 2) nonionic-anionic surfactant selected from the group consisting of nonionic-phosphate, nonionic-sulfate, nonionic-carboxylate and nonionic-sulfonate, and 3) water, wherein the weight ratio of the anionic surfactant to the nonionic-anionic surfactant is 1:0.2 to 10, and the water amount is 0.5 to 9 times as much as the total amount of the surfactant.
The above patent demonstrate some shortcomings: firstly, the microorganism in the above patents is stepwise added to oil recovery layer with other reagents instead of being used with other components, and secondly, no alkaline is used in the present invention.